The ageing process for red wine requires slowly evolving oxidation and reduction reactions over an extended period of time. There are many complex chemical reactions that occur in such a process, and it is important for these reactions to occur naturally at the interface of the surface of wine, in direct contact with wood, such as in a properly filled and coopered barrel. Wood is a semi-porous material, and therefore the quantity of wine within the barrel is reduced by the evaporation of constituent water and ethanol, through pores and joints in the wooden barrel. Subsequently, the volume of wine is naturally shrinking over time at a rate of approximately two to four liters per month, depending on several factors including, but not limited to, temperature, humidity, wood porosity, barrel construction, and the surface area of wine exposed to wood. As evaporative losses occur within a wooden barrel, a “head-space” develops within the barrel, above the wine, and leads to an ever-increasing air-fluid interface, where oxidation occurs that is considered undesirable. This undesirable oxidation not only accelerates the premature aging of wine by complex chemical reactions occurring at the air-fluid interface, but the presence of oxygen within the expanding head-space inevitably leads to microbial growth on the surface of the aging wine. This microbial growth contaminates the wine, promoting off-flavors and spoilage. In an appropriately filled barrel, in which the head-space volume is maintained at a minimum, such contamination is curtailed.
Historically, wooden barrels are the containers of choice in the winemaking industry for storing and aging wine for many reasons. Primarily, the wood imparts flavoring to the wine, and this flavoring varies with the type and quality of the wood. The amount of flavoring imparted to the wine is dependent on the size of the barrel and therefore, the ratio of wine to the inside surface area of the barrel. The age of the barrel is also important, along with the length of time the wine is stored within it. Standard wine barrels are coopered from white oak, and generally contain only about sixty gallons, which is very small, considering the large, industrial constrainments and tanks employed for other beverage processing.
The typical flavor imparting life-span of the standard oak barrel employed in winemaking is considered to be approximately three years. However, more that fifty-percent of the oak's available flavoring is extracted into the wine within the first twelve months of use. Additionally, many wineries employ the use of “neutral” oak barrels, which have been used for more than three years to continue storing some wines, and no longer impart any significant flavors to the wine. Barrel selection depends on the wine varietal, the winemaker's choice and the financial resources of the winery, as the average price for each oak barrel typically exceeds several hundred U.S. dollars.
There are several other reasons oak barrels remain in use today, either in new or neutral condition. As discussed above, slow and desirable oxidation and reduction reactions occur over time, as wine evaporates through the natural pores of the wooden barrel staves and oxygen permeates back through the wood. This slow oxidation is not only desirable but is considered mandatory for creating premium wines. Despite the drawback of creating the aforementioned head space, the desirable oxidation occurring at the interface of wood and wine is considered vital to the production of premium wine.
The term “ullage” is used to describe the loss or leakage of wine from its container. The natural evaporation or loss of wine through the barrel is supplemented by leakage and sampling. In an attempt to control ullage, wineries devote large sums of money to create and operate elaborate humidification systems, and for the labor required to consistently “top-up” the barrels, to minimize head-space. Additionally, the “top-up” wine is often inferior quality, newer wine, which detracts from the flavor of the aged wine within the barrel. However, even the most diligent topping-up fails to eliminate ullage, and the undesirable favoring resulting from head-space oxidation. This effect is magnified, especially when pushing for larger numbers of barrels, as necessary for wineries to achieve an advantage in economic scale of production.
Oak barrels posses other characteristics that ensure their ongoing use in modern-era winemaking, including the natural antiseptic qualities of wood, and the near-absence of electrostatic charges of wood particles. In containers made of stainless steel, for instance, there is a natural stratification or “layering” effect that occurs during wine settling, due to the electrostatic characteristics of metal, which typically mandates filtration for clarification. In addition, the charring of the wooden barrel staves, as typically achieved during “fire-bending” in the coopering process, leads to a slow and natural, charcoal adsorption of impurities from the stored wine.
Therefore, smaller oak barrels are the time-tested container of choice for storing and aging premium wines. However, a system is needed to improve the performance of wood barrels, especially in lager scale wine making operations, still employing the smaller oak barrels. There is a need for more consistent and cost-effective techniques for minimizing head-space in aging barrels, and prevent dilution effects attributable to topping-up, and assure better and more consistent quality in the production of wine.
The following is a disclosure of the present invention that will be understood by reference to the following detailed description taken in conjunction with the accompanying drawings.
Reference characters included in the above drawings indicate corresponding parts throughout the several views, as discussed herein. The description herein illustrates one preferred embodiment of the invention, in one form, and the description herein is not to be construed as limiting the scope of the invention in any manner. It should be understood that the above listed figures are not necessarily to scale and that the embodiments are sometimes illustrated by fragmentary views, graphic symbols, diagrammatic or schematic representations, and phantom lines. Details that are not necessary for an understanding of the present invention by one skilled in the technology of the invention, or render other details difficult to perceive, may have been omitted.